Pilot-Scale Application of Attapulgitic Clay for Stabilization of Toxic Elements in Contaminated Soil

Abstract

This study presents an in situ pilot-scale application of attapulgitic clay for stabilization of toxic metals and metalloids in contaminated soil. The selected field for the pilot-scale experiment was heavily contaminated with toxic metals and metalloids in total (Cu: 122 mg/Kg, Pb: 6,610 mg/Kg, Zn: 3,630 mg/Kg, Cd: 26.3 mg/Kg, Ag: 9.4 mg/Kg, As: 802 mg/Kg, Mn: 1,435 mg/Kg, Ba: 304 mg/Kg, Sb: 95.3 mg/Kg) and leachable concentrations. Geochemical and physical properties of treated soil were thoroughly studied before and after mixing with the attapulgitic clay. Soil mineralogy was determined by X-ray diffraction (XRD) and scanning electron microsope (SEM) techniques. On the basis of the site-specific soil geochemical properties, an appropriate proportion of specific grain-size attapulgitic clay was added and mixed in situ with simultaneous adjustment of soil moisture content to reach saturation. Analytical data of amended soil samples collected 1 month after the application showed a significant reduction of water leachable metal fraction (Cu: 17%, Pb: 50%, Zn: 45%, Cd: 41%, Ag: 46%, As: 18%, Mn: 47%, Ba: 45%, Sb: 29%). In addition, soil pH was stabilized at slightly alkaline conditions and remained constant during a 7-month monitoring period after amending the soil. Overall, the use of attapulgitic clay as a binder for immobilizing metals in contaminated land is a promising stabilization method at a competitive cost under present market conditions.